1. Field of the Invention
The present invention relates to a contact type image sensor which is used in an input apparatus for reading letters and images.
2. Description of the Related Art
An input apparatus for reading letters and images by use of a line sensor is adapted to read two-dimensional information such that the information on an original illuminated by a fluorescent lamp or a light emitting diode (LED) array is image-formed on the light detecting element through an optical lens, a rod lens array or an optical fiber while the original or the sensor is moved.
Such an input apparatus has a construction in a combination form of a charge coupled device (CCD) with an optical lens, or in a combination form of a long image sensor with a rod lens array or an optical fiber array. Especially, the latter so called a contact type image sensor has been in progress of development aiming at miniaturization and reduction in manufacturing cost of the facsimile or the like.
However, most of the above mentioned contact type image sensors perform an image-formation on the light detecting element through a rod lens array, thereby naturally limiting the miniaturization. In this type using a rod lens array, since the light detecting element should be apart from the original by a conjugate length of the rod lens array, which usually makes the thickness of the sensor as a unit as much as 20 mm to 30 mm. Further, in this type, since a lens system is used, an optical adjustment is required, and the chromatic aberration must be considered in case of color reading while the transmission efficiency of light quantity is low.
On the contrary, the sensor using an optical fiber array instead of such a lens system hardly requires an optical adjustment, has enough transmission efficiency of light quantity, and is suitable for miniaturization since the length of the optical fiber array can be reduced because there is no focusing in it. Further, this type using the optical fiber array has an advantage that there is no chromatic aberration in case of color reading. However, a portion of the light, which is incident on the optical fiber at an incident angle larger than the angular aperture of the optical fiber, is not totally reflected at the boundary between each optical fiber core and each clad and is transmitted to an adjacent optical fiber through the boundary as a leakage light. When this optical fiber array transmits an image information, such a leakage light deteriorates the quality of the image.
Accordingly, with an aim for absorbing such a leakage light, an optical fiber array of extra mural absorption (EMA) type, in which light absorbers are interposed between the optical fibers, is proposed. But, if this EMA type is applied to the contact type image sensor, the problem arises that the original to be read can not be illuminated.
As a solution to the above mentioned problem, the present inventors have proposed a method of utilizing, for a contact type image sensor, an optical fiber array substrate constructed by laminating one optical fiber array member, which fiber is coated with light absorber, and another fiber array member, which fiber is not coated with light absorber, in the U.S. application Ser. No. 217,681 filed on Jul. 11, 1988, now allowed U.S. Pat. No. 4,942,481 in Japanese patent application no. 62-179,635 and in the report "A NEW TYPE CONTACT IMAGE SENSOR" presented In the Springtime National General Meeting of the Electronics Information and Communication Academy No. D-134, in 1988.
However, firstly, in the construction of this new type contact image sensor, since each of the light detecting element array and the driving circuit is disposed on its exclusive substrate which is different from the substrate of the optical fiber array, there exists a great number of components in the sensor and thus, there is a certain limitation of miniaturization of the sensor. Secondly, since the substrate of the optical fiber array and the substrate of the light detecting element array are independent from each other, there is needed a positioning process to position the optical fiber array and the light receiving element array with respect to each other during or after assembling procedure.